Combined with the collecting power of the Very Large Telescope, X-shooter is the most sensitive medium-resolution spectrograph currently in operation, allowing us to perform quantitative spectroscopy of objects that, up to now, were deemed too faint. In addition, with its unique wavelength coverage, X-shooter provides access to an un-precedentedly large number of diagnostic lines. We review our recent work on massive stars in Local Group dwarf galaxies and in NGC 55, an irregular galaxy in the foreground of the Sculptor Group. The observations were obtained as part of the ESO Science Verification Programme and the NOVA-Dutch Guaranteed Time Observation Programme. The aim is to investigate the evolutionary status of high-mass stars in various environments and to test the theory of radiation-driven stellar winds at metallicities below that of the Small Magellanic Cloud.